1. Field of the Invention
The present invention relates to an automotive brake fluid pressure control apparatus employed, for example, in traction control during acceleration slippage and in vehicle motion control during turning or the like.
2. Description of the Related Art
Conventionally, as shown in FIG. 18, a hydraulic circuit which drives hydraulic pumps P1 and P2 with a hydraulic motor MR, has employed in an automotive brake fluid pressure control apparatus, for example, in traction control during acceleration slippage.
This hydraulic circuit performs traction control on a vehicle having front-wheel drive (FF) and a front-mounted engine, and valves and the like to perform traction control are disposed in a brake fluid conduit reaching from a master cylinder (M/C) to wheel cylinders (W/C) of left and right front wheels FL and FR. Specifically, the conventinal hydraulic circuit includes master-cylinder cutoff valves (SM valves) which cut off brake fluid from the M/C, reservoir cutoff valves (SR valves) which cut off communication from a reservoir R on the M/C side to the intake sides of the hydraulic pumps P1 and P2, and also electromagnetic-type valves V1 and V2 which perform holding and release of high brake-fluid pressure applied to the W/Cs.
Accordingly, when executing traction control with this hydraulic circuit (hereinafter described with reference to the FL wheel), the braking force was controlled with the holding and release of brake-fluid pressure performed by the valves V1 and V2 in a state where the conduit reaching the valves V1 and V2 had been interrupted by the SM valves, the conduit reaching the intake sides of the hydraulic pumps P1 and P2 had been caused to be communicated by the SR valve and moreover the high-pressure brake fluid had been discharged by driving the hydraulic pump P1.
However, when attempting to initiate traction control as described above at a low temperature, there existed a problem in that an amount of discharge of the hydraulic pump P1 was insufficient, and traction control could not be favorably performed.
That is to say, the viscous resistance of the brake fluid increases at a low temperature, and so there existed a problem in that a sufficient amount of discharge could not immediately be assured, and appropriate traction control was impossible, even in a case where driving of the hydraulic pump P1 was initiated to perform traction control. Moreover, because the conduit reaching from the M/C to the hydraulic pump P1 via the SR valve is considerably long, effects due to low temperature are large, and countermeasures must be taken when the temperature is low.
Furthermore, the need for performing traction increases at a low temperature due to freezing of a road surface and the like, and so countermeasures at low temperature are especially desired.
Additionally, when pump driving was initiated after the occurrence of acceleration slippage in a case where of acceleration slippage is large of even when not at a low temperature, there existed a problem in that control hydraulic pressure was insufficient and the acceleration slippage could not be suppressed immediately, and smooth acceleration to start running could not be performed.